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The aluminum division of Central Motor Wheel of America Inc. (CMWA) approached the Environmental and Energy Systems group of Dürr Systems Inc. in keeping with the company’s green factory efforts and a focus on reducing fuel consumption. The plant was in the midst of a company-wide initiative to reduce energy at both the aluminum and steel wheel divisions.
Dürr targeted the two paint lines and their respective emission control devices at the aluminum division as a basis for the initial evaluation. Each paint line consists of primer and topcoat booths that recirculate a significant amount of air back to the spray booth while a portion of the air is exhausted to a thermal oxidizer emission control system. The air that is exhausted to abatement is then replaced via a fresh air source to the spray booths. Each line is also equipped with primer and topcoat ovens that also exhaust to the oxidizers.
One of the paint lines was equipped with a 15,000 Scfm, high-efficiency Dürr Ecopure RL15 regenerative thermal oxidizer with a thermal energy recovery rating of 95 percent and an average temperature rise across the unit of 100 degrees Fahrenheit. The other line treated its emissions with a 13,000 Scfm recuperative thermal oxidizer with a thermal energy recovery rating of about 55 percent and a temperature rise across the unit of about 580 degrees F. Since both oxidizers treated relatively the same air volume and emission concentration, 11,675 Scfm and 21 pounds per hour on average, the recuperative oxidizer became an area of distinct energy-saving opportunity.
“The recuperative oxidizer probably offered a lower capital cost and improved the bottom line of the initial paint line package investment. However, the inefficiency of the recuperative oxidizer resulted in long-term fuel consumption approaching $500,000 per year based upon today’s natural gas prices,” said Karl Walby of the Dürr EES aftermarket sales team. The comparative fuel consumption costs of the other aluminum line with the Ecopure RL were closer to $65,000 per year.
Since the capacity utilization of both aluminum paint line oxidizers was upward of 84 percent, a new high-efficiency RTO would be required to replace the inefficient recuperative unit, recuperative oxidizer exhaust heat could be recovered to supplement the paint process ovens, or a creative alternative solution would be necessary.
After completing a cost benefit analysis of new replacement equipment vs. secondary heat recovery, the alternative and most beneficial solution existed at the end of the steel division’s paint line, about 200 yards from the aluminum division. The steel division was equipped with a 40,000 Scfm, high-efficiency Ecopure RL40 regenerative thermal oxidizer to treat emissions from a similar paint process as the aluminum division. The capacity utilization of the steel line RTO was only about 35 percent, requiring a nominal 14,000 Scfm of the available 40,000 Scfm. The plant originally expected the utilization of the unit to be greater, but various strategic changes to process formulations, environmental and air balance initiatives have kept the emission control volume of the steel line comparable to the aluminum lines.
The resulting strategy was to optimize the overall emission control scheme for both the aluminum and steel divisions. The project was one of both reconditioning and relocation. The Ecopure RL40 from the steel line would be relocated to treat the combined emissions from both aluminum paint lines, and the inefficient recuperative oxidizer would be removed from service while the Ecopure RL15 would be relocated from the aluminum division to the steel paint line to be operated at about 93 percent of its capacity.
The standardized design of the Ecopure RL was extremely favorable to the project strategy since each system general arrangement closely matched the other. In fact, the existing equipment foundations had both been reinforced to the extent that no changes were required at either site. During the relocation, both units were reconditioned according to Dürr preventive maintenance recommendations. The reconditioning was further simplified and expedited while the units were dismantled for relocation. CMWA handled utility infrastructure changes that were mitigated by the similarity in orientation between the two RTOs.
Most importantly, once the RLs were relocated, the recuperative oxidizer was removed from service and the duct work from the corresponding paint line was re-routed a nominal 180 feet to the newly relocated RL40 along with the first paint line. Even with the combined emissions from both of the aluminum lines, there remains 40 percent spare capacity in the unit if future sources require controls.
The project was successfully executed from start to finish in a remarkably fast six-week schedule from order receipt to completion.
An 80 percent reduction in fuel consumption was achieved with a natural gas reduction of 7.25 million Btu’s per hour and a projected $427,000 per year savings based upon current fuel costs and production hours of operation.
The project moved forward quickly, in part, because the return on the project investment was less than 12 months.